Handle microphone contention/Phone calls while recognition is active

Internally we pause the recognition when:
 - a phone call is active/off-hook/ringing
 - or some other application grabs the microphone

we auto-resume when the condition that caused us to pause reverses.

Both these events are notified to the client via callbacks so that they can choose to display on their UI,
that the recognition is paused for some reason.

Bug: 16515468
Bug: 16740806
Bug: 16514535
Change-Id: Ib274d68522c8cf37d42402c875b16159957657f0